SOC meters for small systems

cptdondo · February 2019

I would like to have a SOC meter on two different systems; one is tiny; 200Ah @ 12V and the other is not much bigger at 600Ah @ 12V. What's a good system these days? A lot RVers use Trimetric but I'm not overly impressed with them as it's strictly a coulomb counter. Any others? I don't really care about monitoring all the different sources; I just want to know how much is left in the batteries.

Estragon · February 2019

There really isn't such a thing as a perfect, or even excellent SOC meter. There are just too many variable, and they'll all tend to drift over a period of partial charge/discharge cycles. The trimetric does have some limited ability to adjust (eg battery efficiency setting), but will still drift. Likewise with WbJr monitoring in MN classics.

IMHO, the only way to accurately measure SOC and monitor battery health in lead acid batteries is with regular SG checks.

"How much is left" is sort of a squishy number as well. If running a big load relative to bank size, the effective watt-hours available will be less than a small load, for example.

cptdondo · February 2019

Oh I know. I spent a summer with a load bank, a 7Ah battery, a bunch of Hall effect sensors, and a crapload of Arduinos learning about SOC, measuring it, compensating for Peukert curves, estimating from current + voltage, I even had SG sensors and I came to the conclusion that I can pick one method that will show 10% SOC and another will show 90% SOC.

So that's why I use squishy terms, because with lead-acid there is no accurate way to really determine the charge of a battery. I'd like to get close, relatively inexpensive, and convenient.

Aguarancher · February 2019

Have you looked at this?

https://www.solar-electric.com/midnite-solar-mnbcms.html

Estragon · February 2019

What did you use for SG sensors?

cptdondo · February 2019

Estragon said:

What did you use for SG sensors?

These guys: https://www.sensorsmag.com/components/fiber-sensing-to-measure-battery-state-charge - the company name is at the bottom of that paper.

The sensors were fragile and pretty reliable. I never moved forward with them as in a mobile environment AGMs make far more sense.

UPDATE: Just checked the website; the sensors are no longer available.

kelperis · April 2019

VictronConnect is what I use

petertearai · April 2019

I use the Victron , seems to be good . Input the % efficiency and Purcurt of the battery . It then makes the required calculations . Still as previously said , it is still only a guide . Not an accurate number .

jonr · April 2019

IMO, the key to accurate SOC via coulomb counting is to have a daily reset to a known state. With a system that adaptively corrects out it's errors for your typical usage.

SOC meters for small systems

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